The invention relates to a method of producing a chain-stitched sewing seam in one or more workpiece plies, and to a sewing unit for performing the method.
The International Standard ISO 4915-1981 (E/F) and the German Standard DIN 61400, German Institute for Standardisation e.V, May 1988 Edition, describe multi-needle chain-stitch sewing stitch types of Classes 400 and 600. A sewing stitch type 406 is accordingly formed from three threads: two needle threads and a looper thread. The two needle threads are guided as loops through the workpiece from the needle side and through two separate loops of the looper thread on the other side of the workpiece. A further loop of the looper thread is guided through the loops of the needle threads and is interlinked with the latter, the interlinkages being drawn against the workpiece.
A further sewing stitch type 407 is formed from four threads: three needle threads and a looper thread. The three needle threads are likewise guided as loops through the workpiece from the needle side and through three separate loops of the looper thread on the other side of the workpiece. A further loop of the looper thread is guided through the loops of the three needle threads and are interlinked with the latter, the interlinkages being drawn against the workpiece.
These sewing stitch types may be formed by, for example, the UNION SPECIAL Class 34700 KF sewing machine, Catalogue No. 282, 2nd Edition (UNION SPECIAL is a Trade Mark).
All the multi-needle chain stitch sewing stitch types of the ISO/DIN classes 400 and 600 have, compared with lock-stitch sewing stitch types, the advantage that they may be formed virtually endlessly by sewing cones, although they also have the disadvantage that, if there is no interlinkage, the seam may become undone in the direction opposite to the direction of the seam.
An object of the invention is to provide a method and a device of the generic type which make it possible to secure the seam in one or more workpiece plies against unravelling, particularly at the end of the seam, that is, to secure it against loosening of the looper thread.